Just installed a cat-back system si/do exiting front of rear tire, on the 4.6L (2.5" piping all the way) Not too happy with the loss of low end power either. I would hate to get rid of the new cat-back system or modify it in anyway.

Would it help any if I installed a 2.25" or smaller pipe between the y-pipe and muffler inlet? Any other suggestions ?

 

Try putting 2.25" pipes exiting in the same location. That should help a little???

 

that would be a great idea, but I was hoping not to tamper with the new tail pipes.
...any other suggestions without modifying the tail pipes?

 

my suggestion: invest in a modification to increase low end torque (a chip perhaps?) your loss in low end torque could not have been too much, and the loss in low end torque shows up at higher rpms. yeah, you do loose low end torque due to less back pressure, but you gain the high end horsepower; in my opinion it should go this way.
i dunno bout the 4.6's, but my 5.4 has too much low end torque even with my (previous owner installed) flowmaster si/do i wish to step up to something even more open to help when I need the power. (flowmasters SUCK! the exhaust can't be more than 3 years old and is rustier than my highschool spanish)
another option is a more restrictive muffler (stock one?) and it should help out.

 

kaliscrew2k2,

Can I ask what might sound like a dumb question, did the dyno sheet show a loss in TQ, or if this SOTP dyno ?

Rocks had a 97 4.6 with a ST ( until he could not stand the sound any more ) and never had any complaint about it. At the second step he was: K&N FIPK and Gibson ST.

I have seen several posts from members talking about TQ loss, when putting on a cat back system.
What the SOTP dyno might be telling your rear end is the stock muffler is not in there acting like a box full of toliet paper blocking up the system. TQ increase is from flow not backpressure as it is some times refered to. You have can the minimum backpressure and still have TQ increase. Hence how high flow cats, headers and a dual system increase TQ and the correlating HP curve ( what is the number 5220, or something like that were the TQ and HP lines cross )

If you search this site, you can find the stock numbers for RWHP, and then spend the $80.00 to $100.00 on the dyno to see where you are at, before making any changes to what you have installed. You might be shocked that you are up over stock.

Just don't want to see you makes changes if the SOTP dyno is the only tool you are using. I have tried the G-Tech, and actually don't trust it, as the driver is part of the times on that, which can skew the numbers, if you are like me. I'm not a consistant enough to use this as a main indicator.

Just some thoughts, trying to save you from doing something that might mess up the flow in the xhst gas run.

Steve